Audio amplifier



G. F. GENAUST AUDIO AMPLIFIER April 3, 1956 Filed March 9, 1955INVENTOR. 6-5024;- Gz-w/wsr BY @mvuanad Jrronuar:

United States Patent AUDIO AMPLIFIER George F. Genaust, Minneapolis,Minn. Application March 9, 1955, Serial No. 493,131 2 Claims. (Cl.179-171) This invention has relation to audio amplifiers and concernsaudio amplifiers capable of amplifying all frequencies and theirharmonics encountered in speech, sounds and music without any apparentdistortion.

In an amplifier made according to the present invention, the output istaken from a transformer, the primary of which is in the cathode circuitof the final stage of an amplifier. A screen grid of a vacuum tube ofthe previous stage is connected through this primary winding to thecathode of said final stage, a control grid of the final stage is tieddirectly to a plate of the preceding stage and a neon glow tube isconnected between the cathode and the control grid in the final stage.

The figure of the drawing is a diagrammatic representation of an audioamplifier made according to the present invention.

Referring to the drawing and the numerals of reference thereon, an audioamplifier made according to the present invention includes a pentode 10,such, for example, as the vacuum tube designated 6SU6; a tube 11connected to operate as a triode such, for example, as the tubedesignated 6V6; and a duo-diode 12 such, for example, as the tubedesignated Y3. The duo-diode 12, a power transformer 13, and a filter 14constitute the power supply and supply the B-plus voltage to theamplifier along a wire 15. This part of the circuit forms no part of thepresent invention.

Audio input is fed to the circuit at terminals 16 and 17 from anysuitable source (not shown). Terminal 17 is grounded and the twoterminals 16 and 17 are connected across resistor 18. A control grid 19of the pentode is connected through an adjustable slider 20 to theresistor 18. Wire is connected directly to a plate 21 of the triode 11and through a resistor 22 to a plate 23 of the pentode 10.

A suppressor grid 24 and a cathode 25 of the pentode 10 are connected toeach other and through a resistor 26 to ground. A control grid 27 of thetriode 11 is directly connected to the plate 23 of the pentode 10. Aprimary Winding 28 of an output transformer 29 is connected at one endto a cathode 30 of the triode 11 and at the other end to a resistor 31.The other end of this resistor 31 is connected to ground and a condenser32 is connected across this resistor. A screen grid 33 of the pentode 10is connected to said primary winding 28 of said output 2,740,835Patented Apr. 3, 1956 transformer 29 at the point where the transformerwinding is connected to the resistor 31.

A neon glow tube 34 is connected between the control grid 27 of thetriode 11 and the cathode 30 of said triode.

In operation, the first or input stage including the pentode 10 is usedas a Class A voltage amplifier with plate and screen voltages equal. Thesecond or output stage including the triode 12 operates as a Class Apower amplifier. This stage offers a very high impedance to the inputfrom the first stage and, therefore, has negligible loading effect onthat stage. In this way, practically the entire voltage gain of theinput stage is effectively utilized. The output transformer 29, in thecathode circuit of the triode 11 has a very low impedance and thereforethere is practically no loss in power transfer in said transformer.

Screen grid 33 of the pentode 10, through its connection to primarywinding 28 of output transformer 29, through the cathode 30 and theplate 21 of the triode 11 is maintained at the same voltage as is theplate 23 of the pentode. Any variations in the supply voltage from thepower supply are reflected back through the triode 11 and the primarywinding 28 of the output transformer 29 to the screen grid 33 to keepthis grid at the same potential as that of the plate 23 of the sametube. The amplified signal is also fed back to the screen grid 33 of thepentode. This results in an output to the output transformer which hasno audible hum or ripple from the power supply to mix with or modulatethe amplified speech or music.

The neon glow tube 34, connected between the control grid 27 and thecathode 30 of the triode 11 serves to prevent arcing between saidcathode and control grid until the triode warms up sufiiciently to startconducting.

What is claimed is:

1. An audio amplifier including a power supply, a first electronic tubehaving a first plate, a first cathode, a first control grid and a screengrid, a second electronic tube having a second plate, a second cathodeand a second control grid, first, second and third resistors, anelectrical connection between said power supply and said second plate,an electrical connection including said first resistor be tween saidpower supply and said first plate, an electrical cconnection betweensaid first plate and said second control grid, first and second inputterminals, an electrical connection between said first input terminaland said first control gn'd, an output transformer, an electricalconnection between said second cathode and a first end of one coil ofsaid output transformer, an electrical connec- 7 tion between a secondend of said coil of said transformer and the first end of said secondresistor and said screen grid, an electrical connection between saidfirst cathode and a first end of said third resistor, a capacitorconnected across said second resistor, and a common electricalconnection between said power supply, said second input terminal, asecond end of said second resistor and a second end of said thirdresistor.

2. The combination as specified in claim 1 and a glow discharge tubeconnected between said second control grid and said second cathode.

No references cited.

